plasma tv out of service

[tom66]

Re: plasma tv out of service

I've never seen that diagram before I guess it must have been reverse engineered.
Vs = Vset probably for R14, otherwise it does not make much sense.

[takara]

Re: plasma tv out of service

you right tom66

Vs = Vset on R14 but I noticed there is no Vs voltage on R24 and R26. It seems that the Vs voltage (183 volt) coming from the power board is defective in some parts of the y sustain board.

The vscan voltage is ok = 115 volt

[tom66]

Re: plasma tv out of service

See if there are any fuses or fusible resistors you could have overlooked?

[takara]

Re: plasma tv out of service

hello tom66

I have already check the fuse from the vs voltage and it is ok. If this fuse did not work, i will not have vscan voltage on the ysustain board

[tom66]

Re: plasma tv out of service

I meant fuses for the Vset voltages, and other voltages, not the Vs fuse.

[takara]

Re: plasma tv out of service

there are two fuses in the y sustain board. one for the vs voltage and the other one for the +5 voltage. there are ok after my measurement.

[tom66]

Re: plasma tv out of service

Can you test the Vset etc. DC-DC packs out of circuit?

[takara]

Re: plasma tv out of service

yes I have made the following measurements and I get :

Vscw = 114 volt
-Vy = - 1 volt
vset = 0 volt

Vs = 183 volt
Va = 65 volt

there are 2 inverters. one for the Vscw and the there one is for Vy. I have change almost all components around the Vy inverter but no result

[Clydeuk]

Re: plasma tv out of service

I believe Vset is the VSet Up which affects the width of a small part of the top of the sustain waveform, if that's the case you may not get a reading, only a scope would tell you if that's working. -Vy should be much more than 1 volt though, sounds like one of the DC DC converters isn't working or it's driving into a short-circuit.

[Clydeuk]

Re: plasma tv out of service

Is that a 50X3 PDP?

[takara]

Re: plasma tv out of service

hello clydeuk

the model of my tv plasma is PDP42V7 from LG

[takara]

Re: plasma tv out of service

hi clydeuk

normally the Vy voltage is -95 according to the specifications. you suggest that the DC DC converters isn't working or it's driving into a short-circuit but I think the second option is more interesting

[Clydeuk]

Re: plasma tv out of service

Oh 42V7, I have one of those panels, working order but very speckly, when I get back home (I'm away a few days) I will see if I can find out more. I'm thinking -Vy where your problem is, whatever the reason why it's not coming up. I need to look closer at mine as it's been a long time, but we could always compare readings between mine and yours. Can't remember if I ever had a diagram for this, I'm thinking probably not.

[Clydeuk]

Re: plasma tv out of service

The -Vy and Vscan (Vsc) I believe the DC converters on this version not on separate sub pcb's but on the main Y Sus PCB. I think IPM failure is less of a problem with these as some of the others, but I only have a small sample to base experience on. I can however when I return home take some resistance readings around the -Vy and the output FET's and and semi's around there, we may get some idea if something is amiss or whether to focus directly on the DC DC section.

[Clydeuk]

Re: plasma tv out of service

Quickly glancing at the diagram you posted I think some fusible resistor or other fusible device has opened depriving some (not all) sections of the Vs supply. Again something could be short-circuit, it can be hard to diagnose these stages in-circuit due to parallel paths, parallel FET's etc. That's an interesting diagram though, it appears to be an abstract of the basic circuitry.

[takara]

Re: plasma tv out of service

hi clydeuk

thank you for your reply


the DC converters for the -Vy and Vscan (Vsc) on this version are on the main Y Sus PCB. I heard the problem is due to the IPM failure so I changed it but no result.

I've found only two diagrams related to the Ysustain board but there are not a full diagram.

[Clydeuk]

Re: plasma tv out of service

This is always a problem that sadly is common nowadays, lack of detailed circuit diagram. I have little doubt you could get it going by fitting a Y-SUS board, however for me it is more interesting to find the exact problem, I grew up repairing CRT sets and by getting in deep to the circuit you gain very useful knowledge which you can use many times and adapt to suit different designs. If in the end you find it's cheaper to replace the whole board than try to source the component(s) then ok. I don't think your problem is IPM related since I think this only provides the basic sustain waveform and the various external circuitry builds on this to achieve the actual waveform required by the display. Can I ask do you still have a picture since replacing the IPM and the accident with the probes?

[Clydeuk]

Re: plasma tv out of service

Do you have the PDP42V7 LG manual? It does not have any schematics but it does show a lot of waveforms together with some general info about the pass top and bottom FET's, they suggest they are failed but the same effect would be seen if they are not receiving the correct supplies or signals. I don't want to waste your time with this manual if you already have one to hand as it doesn't tell us much, but if you don't have it maybe it's something to look over.

[tom66]

Re: plasma tv out of service

Alignment guide for many panels including 42V7.

[takara]

Re: plasma tv out of service

hello clydeuk hello Tom66

I noticed no changes since replacing the IPM . I mean the picture with osd is still dark. the sound is ok. When you switch on the tv, some black stains appears on the screen. After several minutes these stains disappears.

Thanks to the tom66's guide, I'm going to check the pass top and bottom FETs if they are failed or not.